• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.12
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• pp.678-684
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• 2004

Automatic reclosing is a typical protection method in power distribution systems for clearing the temporary faults. However, it has a fatal weakness in regards to voltage sags because it produces successive voltage sags. In this paper, we explored successive impact of voltage sag due to the automatic reclosing of power distribution systems. The actual tests of low voltage loads were accomplished for obtaining the susceptibility of voltage sags. The final results of the test yielded power acceptability curves of voltage sag, and the curves were transformed the 3-dimensional CBEMA(Computer Business Equipment Manufacturer Association) format. For the quantitative evaluation of the impact of successive voltage sags, an assessment formulation using the voltage sag contour was proposed. The proposed formulation was tested by using the voltage sag contour data of IEEE standard and the results of the test. Through the case studies, we verified that the proposed method can be effectively used to evaluate the actual impact of successive voltage sans.

• Parasites, Hosts and Diseases
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• v.58 no.1
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• pp.1-5
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• 2020

Sarcocystosis was diagnosed worldwide by serodiagnostic tests utilising the whole parasite, for which the protozoa were maintained in vitro are more costly. In this study, antigenicity of Sarcocystis falcatula recombinant protein (rSfSAG4) was investigated towards the local communities of Pangkor and Tioman Islands and its seroprevalence was surveyed in these islands. A total of 348 human sera were tested using rSfSAG4 by Western blot and ELISA. High prevalence of sarcocystosis was observed in Tioman Island (80.6%) than in Pangkor Island (50.0%) by Western blot. In ELISA, the seroprevalence observed in Tioman Island was 45.9%, whereas in Pangkor Island 63.0%. In other parasitic infections, the prevalence was 34.0% by Western blot and 46.0% by ELISA. In healthy control group, 7% by Western blot and 8% by ELISA showed positivity to rSfSAG4. It is suggested SfSAG4 is a candidate antigen to measure seroprevalence of sarcocystosis.

• Journal of the Korean Society for Railway
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• v.12 no.5
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• pp.694-699
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• 2009

This paper presents a synchronous-reference-frame-based control of single-phase UPQC(Unified Power Quality Conditioner) to improve power quality in ac electrified railway systems. The proposed synchronous-reference-frame-based UPQC can compensate the voltage distortion, the voltage sag, the harmonic currents, and the reactive power instantaneously. The simulation results show that the UPQC can compensate the harmonic supply voltages, the voltage sag, the harmonic load currents, and the reactive power in electrified railway systems. Validity and effectiveness of the proposed UPQC control method based on the synchronous-reference-frame is illustrated through the simulation results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.3
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• pp.6-11
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• 2006

This paper describes the novel control techniques design of VSC(Voltage Sag Corrector) for the purpose of power line quality enhancement. A fast detecting technique of voltage sag is implemented through the detection of instantaneous value on synchronous rotating dq-reference frame. The first order digital filter is added in the detection algorithm to protect the insensitive characteristics against the noise. The relationship between the total detection time and cut-off frequency of the filter is described. The size of the capacitor bank used as the energy storage element is designed from the point of view of input/output energy with circuit analysis. Finally, the validity of the proposed scheme is proven through the simulated results.

• Journal of Electrical Engineering and Technology
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• v.12 no.3
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• pp.1016-1026
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• 2017

An adaptive extended Kalman filter based on the maximum likelihood (EKF-ML) is proposed for detecting voltage sag in this paper. Considering that the choice of the process and measurement error covariance matrices affects seriously the performance of the extended Kalman filter (EKF), the EKF-ML method uses the maximum likelihood method to adaptively optimize the error covariance matrices and the initial conditions. This can ensure that the EKF has better accuracy and faster convergence for estimating the voltage amplitude (states). Moreover, without more complexity, the EKF-ML algorithm is almost as simple as the conventional EKF, but it has better anti-disturbance performance and more accuracy in detection of the voltage sag. More importantly, the EKF-ML algorithm is capable of accurately estimating the noise parameters and is robust against various noise levels. Simulation results show that the proposed method performs with a fast dynamic and tracking response, when voltage signals contain harmonics or a pulse and are jointly embedded in an unknown measurement noise.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.62 no.4
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• pp.210-215
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• 2013

This paper analyze the bus voltage sags in the power distribution system with a small scale cogeneration system when the superconducting fault current limiter was introduced. Among the solutions to decrease the short-circuit current considering the locations of the small scale cogeneration system, the superconducting fault current limiter (SFCL) has been announced as one of the promising methods to reduce the fault current because the installation of the small scale cogeneration system which increases the short-circuit current. According to the application locations of the small scale cogeneration system in a power distribution system, it has caused the variations of voltage sag and duration which depends on the change of the short-circuit current, which can make the operation of the protective device deviate from its original set value when the fault occurs. To investigate the voltage sag when a SFCL was applied into a power distribution system where the small scale cogeneration system was introduced into various locations, the SFCL, small scale cogeneration system, and power system are modeled using PSCAD/EMTDC. In this paper, the effects on voltage sags are assessed when the SFCL is installed in power distribution system with various locations of the small scale cogeneration system.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.11
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• pp.66-73
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• 2015

AC-based power systems, having the advantages that voltage transformation and long distance transmission are easy, have been constructed since the last 19th century. However, DC-based power system is paid attention these days because of the development of power electronic devices as well as the increase of digital loads and distributed generation. For instance, the transmission systems using High Voltage DC (HVDC) are commercially operated in the world and the researches on distribution system using Low Voltage DC (LVDC) are gradually increased. This paper analyzes voltage sag, resulted from faults, in LVDC distribution system according to the number of poles. Modeling and simulation with various conditions are conducted by using ElectroMagnetic Transients Program (EMTP). Moreover, some countermeasures to reduce voltage sag in LVDC distribution system are suggested briefly.

• Proceedings of the KIEE Conference
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• summer
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• pp.205-207
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• 2004

This paper proposes a new SSHG(Sag/swell and Harmonic Generator) injecting voltage by using series inverter. The proposed SSHG composes series inverter, DC capacitor as energy storage, rectifier and voltage clamp circuit. This SSHG is designed to generate typical power disturbances, such as voltage sag/swell, over/under voltage and voltage flicker. Also it is designed to generate unexpected voltage phase jumping waveform by controlling the series inverter. In this paper, three kinds of control methods for the proposed 2MVA SSHG are given. Typical voltage sag and swell waveforms are implemented by adopting simple control method. Also the voltage flicker is generated by changing the amplitude of the injected voltage in random. Owing to the limited bandwith of the proposed SSHG, high frequency transient waveforms can be obtained by using the open loop control. The simulation and experimental results are given to verify the operation of the proposed SSHG, Finally, conclusions are given.

• Parasites, Hosts and Diseases
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• v.53 no.1
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• pp.125-128
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• 2015

The prevalence and genotype of Toxoplasma gondii infection in dogs in Henan Province, Central China was investigated. A total of 125 blood samples were collected from pet dogs during April to June 2013, and all samples were examined by indirect hemagglutination antibody test (IHA) and nested PCR. The overall T. gondii prevalence in pet dogs was 24.0% (30/125), with 20.8% (26/125) in IHA and 10.4% (13/125) in PCR, respectively. No statistical associations were found between animal gender and age and the prevalence of T. gondii infection. Thirteen positive DNA samples were genotyped using 11 PCR-RFLP markers, including SAG1, (3'+5') SAG2, alt.SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico. Of these, only 2 samples were genotyped with complete data for all loci, and a novel genotype (type III at SAG3 and GRA6 loci, and type I at other loci) was identified. This is the first report of genetic characterization of T. gondii infection in dogs in China.

• Investigative Magnetic Resonance Imaging
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• v.19 no.4
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• pp.224-230
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• 2015

Purpose: To determine whether we should recommend ultrasonography (US) for an incidental thyroid nodule identified by additional cervicothoracic sagittal T2-weighted image (C-T sag T2WI) of lumbar spine magnetic resonance imaging (MRI). Materials and Methods: A retrospective study of 61 patients who underwent both lumbar spine MRI and thyroid US between December 2011 and April 2015 was conducted. For all US-found thyroid nodules > 1 cm, investigators evaluated whether there was any correlation between thyroid nodule detectability by C-T sag T2WI and US features such as echogenicity, composition, or suspicion of malignancy. Results: Solid hypoechoic (2/4; 50%) or mixed echoic nodules (4/8; 50%) appeared to be found relatively more easily by C-T sag T2WI than more benign-looking solid isoechoic (1/4; 25%) or spongiform nodules (0/6; 0%). Among six nodules with ultrasonographic suspicion for malignancy, only one nodule was detected by C-T sag T2WI. Conclusion: If an incidental thyroid nodule is seen by C-T sag T2WI, it would be better to recommend thyroid US for identifying malignancy.